1. The Field of the Invention
This invention relates to internal combustion engines and more particularly, to novel systems and methods for forced-air induction systems.
2. The Background Art
It is often desirable to increase the power output of an internal combustion engine through the use of a turbocharger. Turbocharger systems and methods have been used successfully in many applications for many years.
The turbine wheel of a turbocharger is encompassed by a scroll or volute. The volute acts as a chamber, conduit, and nozzle to direct the flow of exhaust gases, from an internal combustion engine, toward the blades of the turbine wheel to induce rotation. The shaft of the turbine wheel is connected to a compressor wheel that will induce high-pressure air into the intake of the engine as the compressor wheel is rotated. Different volutes are designed for different volumetric flow rates of exhaust gases. The volumetric flow rate of exhaust gases is a function of engine speed. Thus turbocharger turbines operate at optimal levels only within a specific range of engine speeds. On either side of that specific range, the performance of the turbocharger degrades.
Many turbochargers, with multiple volute housings, have included different types of valves and director plates that direct the exhaust gases into specific volutes within the turbocharger housing. At low engine output, this director valve will close off one or more of the volute passages and allow the gases to pass into only one of the smaller volutes. Whereas these valves maintain or increase the velocity of the gases within the volute portion of the housing, they loose a high percentage of the available power as the gases are induced into the annular nozzle of the housing. This loss of velocity occurs as the high-speed exhaust gases are being thrust into the stagnant gases contained in the nozzle opening of the volute that is closed off by the director valve. Without a direct barrier between the two gas chambers this becomes a direct parasitic load on the turbine wheel.
This problem is always present in any turbocharger system containing a director valve and a multi-volute turbocharger housing, because both volute chambers share the same annular nozzle. If the dividing wall between the volutes is extended into the annular nozzle, a wide and turbulent interface boundary is created within the closed volute around the periphery of the turbine wheel. In this opening the high-speed exhaust gases that are immediately encompassing the turbine wheel are colliding with the stagnant gases within the closed off volute. This significantly reduces the impingement velocity of the drive gases against the turbine wheel.
Nozzle rings with fixed directing vanes have been used in turbocharger housings to direct exhaust gases within the annular nozzle of the housing. These nozzle rings have also been used to change the annular nozzle opening to adjust for engine load and speed. There have also been housings utilizing nozzle rings with moveable vanes to adjust for engine load and rotational velocity. These devices are bulky, relatively expensive, and require many moving parts. These moving parts have significant maintenance issues because of the harsh operating environment within the turbocharger housing. This harsh environment is the combined effect of extremely high temperatures and soot, mixed with other abrasive material contained in exhaust gases that are forced through the housing at super-sonic speeds.
What is needed is a device to channel the exhaust gases against the turbine wheel while creating a solid boundary between the high-speed gases used to drive the turbine wheel and the stagnant gases of a closed volute section. In addition to those requirements, the device must be able to adjust for different engine loads without having serious maintenance problems.